This invention relates generally to an apparatus for forming and producing filaments or elongated strands of synthetic material such as fluorocarbon resins that can be used to form yarns which can be woven, knitted, braided or otherwise combined to provide a plurality of products adapted to improve service and life for many conventional applications.
It is well known that fluorocarbon resin fibers and filament such as polytetrafluoroethylene (PTFE); fluoroethylene propylene (FEP) and other polymers and co-polymers are adapted and have been used to form woven and knitted materials because of the chemical and physical properties of such fluorocarbon resins in that they are chemically inert, heat and corrosion resistant, easy to clean, and have a built in lubricity.
For a more detailed discussion of the properties and applications of fluorocarbon resin fibers and filaments reference is herein made to the publication entitled Du Pont Technical Information - Fibers - Bulletin T-13 dated March 1970 which is incorporated herein by reference.
In this Bulletin, it is shown that PTFE fibers and filaments in woven, knitted and braded forms are widely used in many industrial applications and in products where the desirable chemical and physical characteristics of these materials act to improve the function thereof.
For example the woven, knitted and braided materials made from fluorocarbon resin filaments or elongated strands are used for all types of clothing, for filter bags and filtering cloths, at industrial and commercial sites where there are chemical processes, chemicals or waste material of a highly corrosive nature and/or corrosive hot gases or hot liquids; and for applications such as woven self-lubricated bearings; for braided packing, for lacing cord and other electronic industry applications; and for many medical uses.
Various methods for producing PTFE fibers, filaments and elongated strands for making articles are known in the prior art. For many years the making of such articles followed the practices of the textile industries in that the yarns have been made from fibers which are obtained from dispersions of fluorocarbon resins. More recently mechanical techniques have been developed utilizing foil slitting wherein a thin layer of PTFE is skived from a billet of the same material and the layer is then slit into threads or filament by means of suitable slitting jigs. For example one technique of this type is shown in U.S. Pat. No. 2,728,950.
In U.S. Pat. No. 4,025,598 another mechanical method for forming threads, elongated strands, or filaments of PTFE is shown in which the surface of a billet of PTFE being rotated is deformed by a jig to form a plurality of grooves and ridges and then a skiving knife is applied to cut the ridges off to form the desired filament. The filament can be as long as desired and can be drawn off heated and stretched and combined with other filaments to form a conventional multi-filament yarn which can then be utilized to form the woven, knitted or braided material.
The present invention is directed to an improved apparatus for the mechanical forming of PTFE filaments or elongated strands wherein a rotating billet of PTFE is engaged by a cutting tool having a plurality of sized offset cutting edges so that a plurality of separate sized and shaped filaments of PTFE can be simultaneously cut in continuous lengths so that the filaments can be drawn off, joined and stretched in accordance with conventional techniques to form yarns of various thickness.
The broad method of making filaments or elongated strands of fluorocarbon resin in accordance with the present invention permits a variety of techniques and variations to provide a desired shape and size for the filaments as is more fully described hereinafter. Further however it will be understood by those skilled in the art that while this apparatus and method is shown as applied to a billet of fluorocarbon resin material that it is equally appli-cable to other ductile materials such as steel, copper or aluminum. Waste is minimized compared with other methods for producing plastic filaments or "METAL WOOLS".
Further the present apparatus and method can be applied to a simple compression molded billet of fluorocarbon resin which is a cheaper raw material then the raw materials now used in the prior art for making the fluorocarbon fibers to provide the desired yarn for forming the woven, knitted or braided materials of fluorocarbon resin.
The strands or filaments obtained by the method and apparatus of the present invention can be used as cut from the fluorocarbon resin billet or they can be moderately or highly oriented to alter their physical characteristics by calendering or stretching at room or elevated temperatures. Further, because of the versatility of the present apparatus and method the actual dimensions of the filaments or elongated strands can be varied over a wide range by adjusting the pitch and depth of cut of the cutting device for establishing the desired cross-section for the respective filament or elongated strands of fluorocarbon resin.